condensed notes-mech of antibiotic
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These antimicrobial agents usually interfere with bactral physiology (e.g. Macrolids [erythromicine], Clindamycin, Sulfamethoxazole, Trimethoprim, the Tetracyclines, and Chloramphenicol
Bacteriostatic: antimicrobial agents that inhibit growth and/or reproduction of infecting agent, but fail to actually kill the bactra
E.g. the -lactam antibiotics (penicillin & cephalosporin), vancomycin, aminoglycosides (gentamycin), and fluoroquinolones (ciprofloxacin)
Bacteriocidal: Antimicrobial agent capable of causing irreversible dmg or death to organism
Antimicrobials may be bacteriostatic @ low conc but bacteriocidal @ high conc
b/c @ cidal doses, it may be toxic to host tooMost commonly, the inhibitory conc is used to quantitate the activity of an agent against an organism (aka Minimal Inhibitory Concentration [MIC])
A factor that affects whether a drug is bacteriostatic or bacteriocidal is the antimicrobial concnetration @ the site
Distinguish b/w bacteriostatic and bacteriocidal-
Most interfere w/ peptidoglycan synth These agents include the -lactam antibiotics (penicillin, cephalosporin, monobactams, carbapenems) and the glycopeptides (vancomycin)
Polysaccharide portion of peptidoglycan structure is made of repeating units of NAG-NAM
However, -lactam antibiotics, like penicillin, binds irreversibly @ the active site of the enzyme that cross links the peptidoglycan st rands --> bactral cell wall is prevented from forming
The bactral cell wall is complete when crosslink b/w 2 peptide chains + the NAG-NAM backbone
Mech of action:
Penicillin (there are different CLASSES of penicillin)
Cephalosporin (cephalosporins are categorized by "generations"; each generation gets stronger
Monobactams (Aztreonam): active against aerobic gram- bacilliCarbapenems: active against essentially all pathogenic org (these are the tanks of the antibiotics)
4 main -lactams
Glycopeptides (Vancomycin): Effective against ONLY Gram+
Interfere w/ cell wall synthesis (most common)1.
Interfere w/ formation of 30S initiation complex or 50S ribosome = interferes w/ formation of 70S ribosome (found in prokaryo tic cells and not euk)Block the elongation process of assembling amino acids into a polypeptide
Can interfere w/ protein synthesis of bactra by:
Aminoglycosides (gentamycin, tobramycin, amikacin, streptomycin): interferes w/ 30S [bacteriocidal]
Linezolid: binds to 23S portion of the 50S subunit [bacteriostatic]; however, should only be used against Gram+ bactra that a re resistant to other antibioticsMacrolids (erythromycin, azitheromycin, clarithoromycin): Acts by binding to 23S rRNA of the 50S subunit [bacteriostatic]
Lincosamides (clindamycin): similar to macrolidsChloramphenicol: binds 23 rRNA; special note for this is that it is effective against many Salmonella; this is used when othe r antibiotics are contraindicated [bacteriostatic]
Tetracyclines: inhibit bactral protein synth by blocking 30S subunit [bacteriostatic]
Main antibiotics that interfere in this way:
Interfere w/ protein synthesis (second most common mech)2.
Bacitracin (topical): disrupt cytoplasmic membraneAnti-fungals: alter the sterol structure and fxn (cholesterol-like structure found in fungi)
Interfere w/ cytoplasmic membrane fxn3.
Quinolones/fluorquinolones (ciprofloxacin "cipro", levofloxacin, norfloxacin): inhibit DNA gyrase or topoisomerase req for DN A supercoiling [bacteriocidal]
Metronidazole: metabolic cytotoxic byproducts that disrupt DNA [bacteriocidal]
Interferes w/ DNA
Used for TBRifampin: binds to DNA-dependent RNA polymerase --> inhibit RNA synthesis [bacteriocidal]
Bacitracin (topical): inhibit RNA transcription [bacteriocidal]
Interferes w/ RNA
Interfere w/ nucleic acid synth4.
Sulfonamides [bacteriostatic] and Dapsone [bacteriocidal]: prevent synth of folic acidTrimethoprim: prevent synth of folic acid [bcateriostatic]
Used to treat UTI, middle ear infections, bronchitis, traveler's diarrhea, and shigellosis
Triimethoprim + Sulfamethoxazole used in combination: synergistic effects cause bacteriocidal
Interfere w/ metabolic pathway5.
Antibiotics inhibit or kill bactra by one of 5 main mechs
List the 5 modes of action of antibiotics drugs on the bactral cell, and give an example of each-
Learning Objectives
Condensed NotesSaturday, August 23, 2014 8:57 PM
Microbiology Page 1
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